The existing handover process that each User Equipment (UE) needs interaction of dozens of messages to perform each handover process. X2 handover process via macro base stations (that is enhanced Node Bs: eNBs) is more optimal than S1 handover via a management Entity (MME) and a Serving Gateway (S-GW) of a core network, whereas Relay Node (RN) and UE both are moving on the train advancing at a high speed, and if multiple UEs simultaneously perform handover process, it will lead to unnecessary resource waste for network and will easily lead to failure of handover process. In order to solve the problem of low handover success rate and improve the efficiency of handover, the concept of group mobility is set forth, but there is no specific solution about how group mobility does now.
If RN and UEs served by the RN simultaneously perform handover process, how to ensure coordinated work is also a problem that cannot be ignored.
In addition, there are two other problems:
Problem one: When RN moves from one another macro base station (that is Donor eNB: DeNB) to another DeNB (target DeNB), MME to which the target DeNB connects may be different from the MME to which the source DeNB connects. So the problem is how to select MME serving the UE, how to transmit context information of UE, and how to establish user plane transmitting path at network side for UE.
Problem two: how to let UE know the change of information at network side, e.g. change of Global Unique Temporary Identifier (GUMMEI) of new serving MME, and generally GUMMEI is included in the Global UE Temporary identifier (GUTI) that MME allocates to UE.
Therefore, it is necessary to provide an effective technical solution to solve group movement and group handover.